Ultrasound-guided interventional procedures such as breast biopsies and prostate brachytherapy are well-known. Needles can be inserted into the body and either obtain a biopsy sample or deliver a dose of a selected therapy. For biopsies, it is desirable to target a specific volume when obtaining a tissue sample. Where a dose is being administered to a target volume, it is desirable to track the precise location of the needle delivering the dose in real-time to ensure that the therapy is delivered according to plan.
Radioactive seeds can be used as a therapy to treat tumors in prostates. In order to ensure adequate coverage of the therapy, it is desirable to implant the seeds a pre-determined distance apart. If the distance between the seeds is too large, tissue between the seeds may not receive the amount of therapy needed for the treatment. If, instead, the seeds are too closely positioned, the tissue can be over-exposed. In conventional brachytherapy, a template having a plurality of holes for guiding needle placement is used. The needle trajectories obtained using these holes are parallel. Where the target volume is of an irregular shape or is blocked by another anatomical feature, the use of such parallel trajectories can provide results that are less than desirable, especially where there is interference from the pubic arch. One of the results of such issues are “cold spots”, or areas with less-than-desired therapy. More recent templates have been suggested that provide for oblique trajectories, but the trajectories are fixed and may not provide results that are desirable in many cases.
The use of robots has been suggested to provide oblique trajectories in brachytherapy. The methods proposed, however, provide less-than-desired results in some circumstances. For example, the systems disclosed by U.S. Pat. No. 6,505,065 to Yanof et al. and by “Robotically Assisted Prostate Brachytherapy with Transrectal Ultrasound Guidance—Preliminary Experiments”, by Fichtinger et al. require that a physician manually position a robotic assembly that inserts a brachytherapy needle. The manual positioning of the robotic assembly is labor-intensive and slow, and is prone to human error.
Factors such as prostate motion, bleeding and swelling during implantation, TRUS imaging artefacts, migration of the seeds in the needle tracks, and needle deflection contribute to errors between the preplan and the actual prostate dose distribution. Thus, verification of the actual locations of the seeds relative to the prostate margin, rectal wall and bladder is needed intra-operatively to allow adjustments to the plan to correct for potential “cold spots” (dynamic re-planning). Intra-procedural re-planning reduces the probability that one or more additional brachytherapy procedures need to be performed by monitoring the implanted dose and adjusting the dosimetry accordingly. Such follow-up procedures are complex in that the patient must be placed in the same position as for the original procedure, there may have been shifting, swelling or changes in the shape of the prostate since the original procedure.
Re-planning the dosimetry of the brachytherapy is currently difficult when performed using CT, in which case the re-planning can typically be performed only once due to the radiation concerns and the time associated with the CT procedure. If, instead, ultrasound imaging is used, the image data is generally insufficient to permit an accurate re-plan even with the advent of “echoseeds”.
Seed segmentation in US images is extremely difficult primarily for 4 reasons: (i) calcifications and other echogenic structures can mimic the bright seed appearance, making seed identification difficult, (unlike the situation in a CT); (ii) there are many seeds—typically 80-100 are implanted; (iii) the seed brightness in the US image varies, depending on its orientation relative to the transducer (much brighter when oriented parallel due to specular reflection); and (iv) the small bright appearance of the seeds are superimposed on a highly cluttered background.
Seed segmentation is an active investigation area in medical image analysis. Most of the reports were concentrated on localization of the seeds in CT or fluoroscopic images. One approach to solve this problem involved the use of multiple projections of fluoroscopic images as a means to reconstruct the 3D positions of the seeds. Since the projection of the seeds overlapped in the images, complicated seed image matching algorithms were required. Another approach is to use 3D CT images. Due to the spacing between CT slices, typically 1 to 5 mm, the same seed may appear in different slices, requiring correction.
Compared to seed segmentation in fluoroscopic or CT images, the challenges of seed segmentation in 3D transrectal ultrasound (TRUS) images are: 1) low contrast-to-signal ratio due to speckle in 3D TRUS images; 2) image brightness of a seed depends on the direction that the longitudinal axis of the seed is with respect to the ultrasound transducer; and 3) high voxel grey values produced by intra-prostatic calcifications or needle tracks.
Further, with the constraints of parallel trajectories, a re-plan may not provide the desired dose therapy with the fewest number of remaining needle insertions.
It is, therefore, an object of the present invention to provide a novel apparatus and computing device for performing brachytherapy and methods of imaging using the same.